For machining metallic materials such as cast iron, use is made of coated tools. The tool wear depends substantially on how resistant the tool cutting edge is to the detachment of individual fragments or the formation of cracks. If parts of the coating have already been detached during cutting, the wear progresses more quickly, and therefore the tool becomes unusable after a short time. Significant importance is attached to the selection of the coating since the layer properties significantly determine the wear progression. Thus, tools consisting of a cemented carbide substrate body which is coated with a plurality of layers by means of CVD have been proposed in the past, for example. Possible coatings consist, for example, of TiCN and an outer layer of α-Al2O3. Similarly, a series of PVD coatings based on the material system TiAlN are known.
By way of example, DE 601 04 709 T2 describes the atomization of a sputtering target by bombardment with gas atoms and/or ions. The sputtering target used is, for example, a titanium plate, in which aluminum plugs have been inserted into existing boreholes. Atoms from the plate itself and from the plugs in the plate are evaporated from the surface of the sputtering target by the gas ion bombardment and change into the gas phase. When a Ti/Al sputtering target is used in a nitrogen atmosphere, a TiAlN layer containing approximately 25 atom % of both titanium and aluminum and up to 50 atom % nitrogen deposits on a substrate body, which can consist, for example, of a cemented carbide. In the case of smooth-faced Ti/Al sputtering targets, greater evaporation rates arise for aluminum than for the titanium, which has the effect that the aluminum plugs in the titanium plate wear away significantly more quickly than the plate itself. In order to provide a remedy here, it is proposed to select the shape of the exposed surface of the plugs in such a way that sputtering rates required for the desired layer composition are established for each metal upon atomization of the target. In particular, the surfaces of the plugs made of aluminum are inwardly curved.
In order to ensure uniform material removal, WO 2004/059030 A2 proposes evaporating the metallic proportion of the hard material layer from alloyed sources, the targets or cathodes.
US 2009/0130434 A1 proposes a coated tool consisting of a substrate body and a hard material coating which, in turn, contains two individual layers, of which the first has a thickness of 0.1 μm to 1 μm and consists of granular crystals with a mean crystal diameter of 0.01 to 0.1 μm, and the second layer has a thickness of 0.5 to 10 μm and is composed of columnar crystals which have grown in a direction perpendicular to the substrate body. The columnar crystals have a mean crystal width of 0.05 to 0.3 μm (in the direction parallel to the substrate body), the mean crystal width being greater than the mean crystal diameter of the first layer.